In pursuit of high-efficiency, environmentally friendly energy production, solid oxide fuel cell (SOFC) technologies have emerged as a potential alternative to conventional turbine and combustion engines. Fuel cell technologies typically have a higher efficiency and have lower CO and NOx emissions than traditional combustion engines. In addition, fuel cell technologies tend to be quiet and vibration-fee. Solid oxide fuel cells (SOFCs) have an advantage over other fuel cell varieties. For example, SOFCs may use fuel sources such as natural gas, propane, methanol, kerosene, and diesel, among others because SOFCs operate at high enough operating temperatures to allow for internal fuel reformation. However, challenges exist in reducing the cost of SOFC systems to be competitive with combustion engines and other fuel cell technologies. These challenges include lowering the cost of materials, improving degradation or life cycle, and improving operation characteristics such as current and power density.
A typical SOFC has an electrolyte made from an expensive, high-purity, chemically co-precipitated stabilized zirconia. Chemically co-precipitated stabilized zirconia may also be used in a porous support tube structure or doped with nickel to produce a fuel electrode (anode). Other expensive materials such as doped lanthanum manganite have been proposed as an air electrode (cathode). The cathode can also be made of a composite of doped lanthanum manganite and stabilized zirconia.
In addition to the cost of materials, conductivity degradation in the electrolyte should be considered. Typically, chemically co-precipitated stabilized zirconia-based electrolytes degrade at a rate as high as 0.5 percent per thousand hours of operation. This degradation has been attributed to gradual changes in the crystalline structure of the solid electrolyte and/or reaction with impurities. Degradation may also occur through on-and-off cycling. On-and-off cycling cycles temperatures, creating temperature differences between components during cooling and reheating. Even small differences in expansion coefficients among various components of an SOFC lead to cracks, flaws, and separations during cycling. These cracks, flaws and separations degrade conductivity and increase resistivity between components. Lost conductivity, increases in resistivity, and degradation of contact surface also lead to a reduction in operating voltages and current densities. As a solid electrolyte degrades, its resistance increases, detracting from the potential of the fuel cell. In addition, increases in resistance in the electrolytes, electrodes or interconnects reduce the power output. As a result of degradation, the expensive fuel cell components are replaced more frequently, leading to higher overall energy costs.
As such, many typical fuel cell systems suffer from deficiencies in providing a low cost alternative to other energy sources. In view of the foregoing, it is considered generally desirable to provide an improved SOFC having electrode and electrolyte materials having suitable properties for use in demanding SOFC applications.